1. Field of the Invention
This invention relates to a signal processing apparatus, and to a method for predicting the result of processing of the apparatus, and more particularly, to a signal processing apparatus for processing a signal formed by very small number of quanta, and to a method for predicting the result of processing of the apparatus.
2. Description of the Related Art
In conventional information processing apparatuses, information is represented by a signal having a continuous waveform, and the signal is processed by various elements. At that time, an input signal branches, in some cases, into a plurality of signals if necessary, and each of the signals branched is processed by the element in branch circuit.
In the current area of multimedia, when receiving and transmitting high-quality image information on an information communication network, the amount of information to be processed in unit time greatly increases at a terminal device of the network. Accordingly, the degree of integration of devices for processing the information more and more increases, and the line width of signal processing circuits becomes narrower. Parallel processing of information will be more frequently performed.
In such a case, the intensity of a signal transmitted through a circuit becomes weaker, and the signal cannot be represented by a continuous waveform as in the conventional apparatuses, but is formed by respective quanta which are discretely distributed on the time base, as a quantum-pulse-train signal shown in FIG. 6. In FIG. 6, each region surrounded by broken lines represents a signal with a rectangular waveform, and each pulse indicated by a solid line represents a quantum. In order to perform signal processing, a quantum circuit which divides such a quantum-pulse-train signal into two signals will now be considered.
Usually, in the stage of designing a quantum circuit used under various circumstances, even when an element to which a signal after branching is input generates quantum noise, in order to check if the element has a sufficient function, it is necessary to know the quantum-pulse-train signal to be input to the element.
The lowest limit of the intensity of a signal for which a circuit incorporating such signal processing elements works well becomes reference when determining an input signal intensity for using an apparatus incorporating the circuit with high reliability, and supply of a signal having an intensity more than necessary can be thereby avoided. Hence, this knowledge concerning the lowest limit of the signal intensity is very important also from the viewpoint of energy saving.
In conventional techniques, however, when a quantum-pulse train shown in FIG. 6 enters a branching point, it is impossible to predict each signal of quantum-pulse train which should be enter into each branch circuit. This is because according to conventional quantum mechanics, when a quanta enters a branch point, it is prohibited to consider that the quanta enters certain one of branch circuits.
That is, according to Dirac, when a photon is incident upon an interferometer, it must be considered that a single photon is divided into two components into which the photon enters (see P. A. M. Dirac "The principles of Quantum Mechanics" (Oxford University Press, London, 1985) 4th ed., pp. 7-9). This indicates that the concept that the photon enters only a certain one of the components is invalid. The same holds true also for other quanta than a photon.